The Croeseid, anciently Kroiseioi stateres, was a type of coin, either in gold or silver, which was minted in Sardis by the king of Lydia Croesus (561–546 BC) from around 550 BC. Croesus is credited with issuing the first true gold coins with a standardised purity for general circulation, and the world's first bimetallic monetary system.

Before Croesus, his father Alyattes had already started to mint various types of non-standardized coins. They were made in a naturally occurring material called electrum, a variable mix of gold and silver (with about 54% gold and 44% silver), and were in use in Lydia, its capital city Sardis and surrounding areas for about 80 years before Croesus' reign as King of Lydia. The unpredictability of electrum coins' composition implied that they had a variable value, which greatly hampered the development of standardised coinage. The royal symbol stamped on the coin, similar to a seal, was a declaration of the value of the contents in gold, silver or electrum.

Herodotus mentioned the innovation of coinage, and standard coinage, made by the Lydians:

So far as we have any knowledge, they [the Lydians] were the first people to introduce the use of gold and silver coins, and the first who sold goods by retail.

— Herodotus, I.94

Croesus replaced all the electrum coins by gold and silver coins using a single coin type: the facing foreparts of a lion and a bull. Compared to later copies made by the Achaemenids, the original Croeseid use a more natural rendering of the two animals. The reverse was struck with two incuse squares. The coins were minted in Sardis. The gold and the silver were refined in Sardis from raw electrum in workshops in Sardis. Recent archaeological excavations have shown stratigraphically that the first Croeseids were indeed issued by Croesus before the Achaemenid invasion, and not after the Achaemenid as has sometimes been suggested.

The gold coins had an initial weight of 10.7 grams. The silver coins also were issued in 10.7 grams, together with many smaller denominations, from 1/3 to 1/48. This makes it the world's first bimetallic monetary system though the idea of smaller silver denominations had originated in Cyme (Aeolis) under Hermodike II.

Soon after however, the gold coins were struck in a lighter standard of 8.1 grams. The modification of the weight may have been the result of a policy to exchange and remove all electrum coins in circulation with the heavier format, the 10.7 grams corresponding to the nominal weight of gold in a standard 14.1 grams electrum stater (about 70%). Once this was done the coins were lightened to 8.1 grams corresponding to the true weight of gold in the electrum coins, which had often been voluntarily debased. Reducing the weight of the gold stater to 8.1 grams also allowed to simplify the exchange mechanism between gold and silver, as now 1 gold stater of 8.1 grams corresponded precisely in value to 10 silver staters of 10.7 grams, or to 20 silver coins of 5.35 grams (weight of the future Achaemenid Siglos), since the current exchange rate on a weight basis was 1 to 13.3 at the time.